The B cells which express immunoglobulin receptors specific for an individual antigen are highly effective for the presentation of this antigen (Rock et al. C., J. Exp. Med. (1984) 160; 1102; Hutchings et al. Eur; j; Immunol. (1987) 17: 393). For example, specific B cells can present tetanus toxin to T cells at antigen concentrations 10.sup.4 times lower than those required for the presentation by non-specific B cells or peripheral blood monocytes (Lanzavecchia, Nature (1985) 314:537).
In addition, in vivo studies with mice deficient in B cells show that these cells are required for the activation of T cells of lymphatic ganglions (Janeway et al., J. Immunol. (1987) 138:2848; Kurt-Jones et al. A. K. J. Immunol. (1987) 140:3773).
Mice deficient in B cells also show reduced responses with respect to specific CD4.sup.+ and CD8.sup.+ T cells from tumors, after immunization with Freund's murine leukemia virus (Schultz et al., Science, (1990) 291).
The capacity of B cells to modify and to present the antigen with a view to recognition by CD4.sup.+ helper T cells restricted by the class II major histocompatibility complex (MHC) forms the basis of a model for the activation of the B cells by T cells (Noelle et al., The Faseb Journal (1991) 5:2770).
The recognition of the peptide-class II MHC complex by CD4.sup.+ helper T cells on the surface of the B cells leads to the formation of physically stable conjugates between the T cells and the B cells (Kupfer et al. S. J., Proc. National acad. Sci. USA (1986) 83:6080).
This direct recognition results in the proliferation and the differentiation of B cells in response to lympholines such as Interleukin-2, Interleukin-4 or Interleukin-5.
The induction of the antibody response against an antigen requires the presentation of the antigen by the B cells.
The majority of the studies on antigen presentation have been carried out using soluble proteins such as tetanus toxoid, lysozyme, hemocyanin (LH). However, most of the antigens to which the immune system is exposed are contained in complex particulate structures such as bacteria or parasites.
It is well known that cells which are capable of phagocytosis such as the macrophages can present bacterial antigens to T cells.
However, it is not known whether cells which do not phagocytose, such as B cells, can present complex antigens of significant size.
It has recently been shown that, in vivo, bacterial antigens must be in a soluble form in order to induce an antibody-dependent response by the T cells (Leclerc et al., J. Immunol. (1990) 144:3174; Leclerc et al., J. Immunol. (1991) 147:3545).
However, it seemed advisable to determine also that, in vivo, bacterial protein antigens are exclusively presented to the T cells by the phagocytic cells and that the B cells cannot modify antigens in particle form.
The study of antigen presentation and the induction of the cellular and/or humoral T response is of particular scientific and medical importance.
In fact, directing the response towards a purely cellular response or a purely humoral response could allow vaccination against certain pathogens, modification of certain biological dysfunctions and curing certain pathologies.
For example, such direction would enable the elimination of persistent infections or the regulation of allergic responses.
In addition, there are two sub-populations of CD4.sup.+ T cells, Th1 and Th2, which have different capacities to produce various lymphokines (Mosmann; Cherwinski, Bond, Giedlin and Coffman, J. Immunol., 136, 2348-2357 (1986)). The induction of Th1 or Th2 plays a major role in the resistance to bacterial, parasitic or viral infections. Thus, in the case of murine cutaneous leishmaniasis, the Th1 protect from infection while the Th2 aggravate the disease. In vitro, B lymphocytes optimally stimulate the proliferation of Th2 clones while a strong proliferation of Th1 clones is observed with adherent cells (Gajewski, Pinnas, Wong and Fitch, J. Immunol., 146, 1750-1758 (1991)).
Directing of the antigen towards presentation by the B cells or macrophages could allow induction of Th1 or Th2 responses.
Various techniques have been developed in the past to achieve a better immune response.
The oldest method consists of activating the immune system with adjuvants. Thus, Freund's adjuvant leads to an increased intensity of the humoral and cellular responses. However, such adjuvants have major disadvantages due to their lack of specificity, toxicity, and immunological side-reactions which may be caused by their lack of purity.
The iscomes (immuno-stimulating complexes) are composed of an antigenic complex and an adjuvant, QuilA, which is extracted from trees. These particles have a diameter of about 35 nm and are composed of sub-units of about 12 nm. They lead to the induction of an immune response but more often the antigens are encapsulated and thus then released in the external medium. In addition, the technique does not allow accurate control of the type of cells presenting these particles, and these particles therefore induce a double humoral and cellular response.
Lastly, from a practical standpoint, these particles are difficulty to prepare, lack stability and have significant toxicity.
Liposomes, which have also been tested for use in inducing an immune response, have the same disadvantages as the iscomes.
Biodegradable microparticles such as for example lactic and glutamic acid polymers have also been developed (Aguado and Lambert, Immuno. Biol., 184, 113-125 (1992)). These particles liberate the antigen in a soluble form during their degradation. This liberation enables presentation of the antigen by different cells and the induction of a humoral response without the possibility of direction towards a specifically cellular response.
Particles composed entirely of recombinant proteins have also been synthesized. Thus, French patent application FR 2 635 532 describes particles composed of a hybrid protein between Hbs antigen and an immunogenic sequence presumed to induce neutralizing antibodies directed against the HIV virus.
Particles containing poliomyelitis toxin have also been produced.
These particles have significant disadvantages. Thus, it is very difficult to insert long sequences into these particles. In addition, they induce as much humoral as cellular response and it is thus not possible to obtain specifically one or the other.
Polyacrolein or polystyrene particles to which antibodies have been coupled have already been used for the development of separation techniques (Rembaum et al., Immunol. (1982) 52:341-351).
However, no use for the preparation of vaccines and in vivo immunization has been reported. The beads used have diameters of 20 to 35 nm (polyacrolein) or of 40 to 120 .mu.m (polystyrene).
Polyacrolein particles of 2 .mu.m diameter have also been used for the in vitro study of T response stimulation (Ziegler et al., Eur J; Immunol. (1987), 17: 1287-1296). The activity of these beads was not tested in vivo.
Porous microspheres (1 to 1000 .mu.m) in which the antigens are immobilized inside the micropores by captation or physical coupling have been disclosed by Cahn in U.S. Pat. No. 5,008,116. In this patent the antigen is progressively released in the circulation and is therefore under soluble form.
In all this work, the size of the particles was not considered to be a critical criterion. Moreover, particles of small size (nanoparticles) such as Hbs particles could be presented by B lymphocytes. On the other hand, particles with too large size (greater than 5-10 microns) could not be presented by phagocytic cells.
The various solutions proposed in the prior art, on the one hand to induce a significant immune response and on the other to direct this response specifically towards one of the two response routes, humoral or cellular, are thus not satisfactory.